Cast flare composition of magnesium dispersed in a matrix,mostly sodium nitrate



United States Patent 3,497,404 CAST FLARE COMPOSITION OF MAGNESIUM DISPERSED IN A MATRIX, MOSTLY SODIUM NITRATE Ralph H. Hiltz, Pittsburgh, Pa., assignor to Mine Safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania N0 Drawing. Filed Jan. 28, 1969, Ser. No. 794,779 Int. Cl. C06d 1/10 US. Cl. 149-17 4 Claims ABSTRACT OF THE DISCLOSURE Cast high-intensity illuminating flares contain a coarse magnesium powder dispersed in a matrix of a solidified salt melt containing principally sodium nitrate with a minor amount of another alkali metal or alkaline earth metal nitrate or nitrite.

This invention relates to pyrotechnic illuminating flares and more particularly to cast flares that emit white light.

Maximum intensity in illuminating flares having magnesium fuel and nitrate oxidizers is achieved using sodium nitrate. This is due to the natural intensity of the sodium spectral line and the sensitivity of the human eye to light of that wavelength. Such flares have been made by compressing miXtures of magnesium, sodium nitrate and organic binders. Tepper, United States Patent 3,370,537, disclosed cast pyrotechnics in which a metal fuel is dispersed in a mixture of oxidizing salts melting below about 250 C. Casting, in addition to being a simpler process than pressing, provides pyrotechnics of high uniformity that burn evenly with constant light output. Since no organic binders are used, the cast pyrotechnics do not show the impact sensitivity of conventional compressed pyrotechnics. Sodium nitrate melts at 308 C. and starts to dissociate at temperatures only slightly above its melting point. Accordingly, molten sodium nitrate or salt mixtures containing a high proportion of sodium nitrate have not heretofore been used in cast pyrotechnics.

This invention is based on my discovery that coarse magnesium powder can be mixed with a salt melt consisting of sodium nitrate and a minor amount of alkali metal or alkaline earth metal nitrite or nitrate, at a temperature up to about 310 C. to form a castable slurry. The slurry when cast into an appropriate casing and allowed to freeze forms a flare of magnesium dispersed in a solidified salt matrix that burns brilliantly and evenly to provide to a steady, high intensity illumination. The burning rate of the flare compositions can be greatly decreased, without decreasing total light output, by addition of minor amounts of lithium fluoride.

The salt melt is principally anhydrous sodium nitrate and contains from about 5-25 of added salt that may be anhydrous alkaline earth metal nitrite, alkali metal nitrite, alkaline earth metal nitrate, alkali metal nitrate other than sodium, suitably calcium nitrite, sodium nitrite, potassium nitrite, calcium nitrate, lithium nitrate or potassium nitrate or mixtures thereof. These mixtures are fully melted at temperatures of about 275-290 C. and can be further heated to about 310 C. without decomposition. It is desirable to heat the mixtures Well above the melting point to increase the fluidity of the melt and facil- ICC itate mixing with the magnesium powder. I have also found that these salt mixtures Wet magnesium and hence are specially easily mixed to form a uniform slurry.

The proportion of metal to oxidizer salt is between about 1 and 1.85 parts metal to each part salt, preferably between 1.25 and 1.50 to 1.

The flares are in use normally ignited at one end and burn lengthwise, the flare life depending on the rate at which the burning front proceeds lengthwise of the flare, designated as linear burning rate. The linear burning rate can be substantially adjusted, suitably from 4-10 seconds per inch, by adjusting the proportion of magnesium to salt, the magnesium particle size and the amount of added salt. Burning rate decreases with increasing amounts of magnesium up to about 60% by weight magnesium and then increases with further increase in magnesium content. Increasing the amount of added salt decreases burning rate with some decrease in brightness. It is presently preferred to use mixtures of calcium nitrate and lithium nitrate as added salts since their use provides increased flare life with a minimum decrease in brightness.

The addition of lithium fluoride to the flare compositions, as a component of the matrix, greatly reduces the burning rate without any decrease in total light output but with, of course, a corresponding decrease in brightness. Any amount of lithium fluoride up to about 10% by weight of the matrix is effective, the higher the amount used the slower the burning rate. This use of lithium fluoride is desirable to meet requirements in which brightness can be sacrificed for longer flare life. For example, flares of this invention that have a life of 30-45 seconds have a life of about seconds when modified by the addition of about 10% lithium fluoride to the matrix.

The flares of this invention are highly resistant to accidental ignition or explosion by ballistic impact. For example, they are non-igniting when struck by .30-caliber ammunition, either ball or armor piercing, fired at a distance of 30 feet or greater. Conventionl compressed flares can be ignited by ISO-caliber ball ammunition at a distance of about 200 feet.

The following examples invention:

Example l.Fifteen parts calcium nitrate and 85 parts of sodium nitrate are heated in a metal furnace pot. The mixture is held at 150 C. for a short time to allow evaporation of the water of hydration of the calcium nitrate. The temperature is then raised to about 300 C., the mixture being completely melted at about 280 C. parts of magnesium powder, passing a 30 mesh (Tyler) and retained on a 70 mesh screen, was added to the molten salt and stirred until a homogeneous slurry was obtained. The slurry was poured into an aluminum casing and allowed to freeze. The resultant solid flare, weighing 350 grams, was 7 inches long and burned for 35 seconds giving 250,000 candles of light.

Example 2.The procedure of Example 1 was repeated using 155 parts of 30-70 mesh magnesium, and a salt mixture of 20 parts NaNO and 80 parts NaNO The resultant cast flare, 7 inches long and weighing 350 grams, burned for 25 seconds providing 375,000 candles of light.

Examples 3.-The procedure of Example 1 was repeated using parts magnesium, 15 parts LiNO 10 parts Ca(NO and 75 parts NaNO The resultant cast flare, 7 inches long and weighing 325 grams, burned for 45 seconds giving 280,000 candles of light.

are illustrative of the I claim:

1. A flare composition consisting essentially of about 1 to 1.85 parts of magnesium particles larger than about 70-mesh dispersed in 1 part of matrix consisting essentially of solidified molten-salt mixture containing sodium nitrate, between about 0 and 10% lithium fluoride, and between about 5 and 25% a member selected from the group consisting of calcium nitrate, lithium nitrate, potassium nitrate, calcium nitrite, sodium nitrite, potassium nitrite and mixtures thereof.

2. A composition according to claim 1 having between about 1.25 and 1.50 parts magnesium per 1 part of matrix.

3. A composition according to claim 2 in Which said member is calcium nitrate.

4. A composition according to claim 2 in which said member is a mixture of lithium nitrate and calcium nitrate.

References Cited UNITED STATES PATENTS 534,557 2/1895 Gerhard 149-20 3,325,316 6/1967 MacDonald 149 17 3,370,537 2/1968 Tepper 149 17 X 3,421,954 1/1969 F'HlCOlleI 149-17 10 CARL D. QUARFORTH, Primary Examiner STEPHEN J. LECHERT, JR., Assistant Examiner US. Cl. X.R. 

